When that happens I always just click “New Tor Circuit for this Site” repeatedly, until I get one of the other two forms of CAPTCHA, both of which are solveable.
I used to try to solve the hard ones, but I found I could not do it; it’s most often impossible to guess what all the letters are in the garbled mess with inverted blobs on top. From your example, I think it’s supposed to be “Thtllyt nthrwhyy”, but I’m usually wrong.